The field of the invention is dimensionally stable yarns.
Polyester multifilament yarns have found widespread use in various applications, and with increasing demands on mechanical performance of such fibers various high-strength polyester yarns have been developed with, among other improved parameters, relatively high modulus and relatively low free shrinkage.
For example, Nelson et al. describe in U.S. Pat. Nos. 5,067,538 and 5,234,764 methods and compositions for a polyester multifilament yarn having a dimensional stability of E4.5+FS of less than 11.5% and a terminal modulus of above about 20 g/d. Among other desirable qualities, Nelson""s yarns can typically be employed in environments with relatively high temperatures (here: 80-120xc2x0 C.). Furthermore, crystallization of the poly(ethylene terephthalate) (PET) in Nelson""s yarns appears to occur during spinning, thereby potentially rendering at least some of the desired mechanical qualities of the yarn independent from fluctuations during drawing.
In another example, Rim et al. describe in U.S. Pat. No. 5,397,527 methods for producing a multifilament yarn fabricated from poly(ethylene naphthalate) (PEN) or other semi-crystalline polyester having a dimensional stability (EASL+Shrinkage) of less than 5% and a tenacity of at least 6.5 g/d. Rim""s yarns advantageously improve several mechanical qualities of previously known PEN yarns and may even be produced using equipment without high-speed spinning capability. However, in order to achieve most of the improvements in mechanical quality, the chemical composition of such yarns is typically limited to PEN or compositions with high quantities of PEN.
In a further example, U.S. Pat. No. 5,238,740 to Simons et al. a polyester yarn with a tenacity of at least 10 g/d and a shrinkage of less than 8% is produced by passing the spun filaments through a heated and insulated column in which a particular temperature profile is employed in combination with relatively high take-up speeds to obtain the desired improved mechanical properties. While Simons"" methods generally produce yarns with a relatively high tenacity and a relatively high secant modulus (greater than 150 g/d/100%) at a comparably low shrinkage, relatively expensive equipment and additional process controls for the heated column are generally required.
Although various compositions and methods for production of dimensionally stable yarns are known in the art, all or almost all of them require moderate to high cord twist for use in demanding fatigue applications such as tires. While global requirements for fatigue resistance have become increasingly stringent, there has not been the commensurate improvement in fatigue resistance to avoid the need for higher twist in the most demanding applications. There have been various approaches to improve fatigue resistance in dimensionally stable yarns (see e.g., U.S. Pat. No. 4,101,525 to Davis, U.S. Pat. No. 4,975,326 to Buylous, U.S. Pat. No. 4,355,132 to East, U.S. Pat. No. 4,414,169 to McClary, and RE 36,698 to Kim). However, all or almost all past attempts have focused on yarns with a DPF of lower than 5 since it was generally believed that increasing DPF decreases fatigue resistance (see e.g., Baillievier U.S. Pat. No. 5,285,623). Furthermore, it is believed that in many yarns fatigue strength retention tends to decrease or remain substantially the same as the filament count increases.
Also, PET treated cords have been produced using Hoechst T748 with a DPF of 7.2, which exhibited similar fatigue resistance when compared to treated cords from a 4.8 DPF yarn. Thus, there is still a need to provide compositions and methods for production of dimensionally stable yarns with improved fatigue strength retention characteristics.
The present invention is directed to compositions and methods for products comprising a dimensionally stable polymeric multifilament yarn with a DPF (decitex [1 denier=1.1 decitex] per number of filaments) of at least 7.5. Especially contemplated yarns include those having a fatigue strength retention FR, wherein the yarn is spun and drawn such that FR increases when DPF increases.
In one aspect of the inventive subject matter, contemplated yarns have a DPF of between about 10 and 20, and comprise a polyester, preferably poly(ethylene terephthalate). It is further contemplated that such yarns have a dimensional stability defined by Ex+TS of no more than 12, more preferably of no more than 11, and that the increase in strength retention per DPF in the contemplated yarns is no less than 1%. Typically, first generation yarns have Ex+TS in the range of 11-12, and later improved versions are lower. Ex is the elongation at x stress for the yarn, where x is 41 cN/tex or, for example, 45 N for 1100 decitex yarn, 58 N for 1440 decitex yarn, 67 N for 1650 decitex yarn, and 89 for 2200 dtex yarn. TS is thermal shrinkage.
In another aspect of the inventive subject matter, contemplated yarns are twisted into a cord or twisted as single yarns that are at least partially disposed within a rubber.
In a further aspect of the inventive subject matter, a method of forming a yarn has one step in which a polymeric material is provided and spun into a plurality of filaments. In a further step, a dimensionally stable yarn is drawn from the plurality of filaments, wherein the yarn has a decitex per filament count DPF of at least 7.5 and a fatigue strength retention FR, and wherein the yarn is spun and drawn such that FR increases when DPF increases.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawing.
FIG. 1 shows the fatigue Strength retention vs. The dectex per fialment.
The inventors have surprisingly discovered that dimensionally stable yarns with excellent fatigue resistance can be produced from a plurality of polymeric filaments with a DPF of at least 7.5. In further preferred aspects, the yarn is spun and drawn such that the fatigue strength retention of the yarn increases when DPF increases.
In an especially preferred aspect of the inventive subject matter, a yarn with 11 decitex per filament was produced by extruding a polyester (most preferably poly(ethylene terephthalate)) from a spinneret into a plurality of individual filaments at a predetermined extrusion rate (typically between about 25.0-80.0 kg/hr) into a gaseous delay zone. The filaments are subsequently solidified in a gaseous quenching column to form an undrawn dimensionally stable yarn with a birefringence of between about 0.02 to about 0.15, and more preferably between about 0.05 to 0.09. The undrawn yarn is then continuously transported to a series of draw rolls where it is drawn to within 85%, preferably within 90%, of its maximum draw ratio at yarn temperatures between about 70xc2x0 C. and about 250xc2x0 C. Typical processes and equipment are described in U.S. Pat. No. 5,630,976; U.S. Pat. No. 5,132,067; U.S. Pat. No. 4,867,936; and U.S. Pat. No. 4,851,172.
With respect to the polymer it is contemplated that numerous polymers are suitable for use in conjunction with the teachings presented herein, however, particularly preferred polymers include various polyesters, and especially poly(ethylene terephthalate). The intrinsic viscosity of preferred polymers is at least 0.7, more typically at least between about 0.85 and about 0.98, and in some cases between about 0.99 and about 1.30, and even higher.
Depending on the desired number of filaments in the yarn, the configuration of contemplated spinnerets used in the melt extrusion process will vary considerably. It is generally contemplated that the number of orifices in the spin pack is not limiting to the inventive subject matter and may thus be most typically between 20 and 150 for 1100 decitex yarns and proportionate to achieve equal DPF for other decitex yarns. However, where yarns with relatively low filament count are desirable, the number of orifices may be between 5 and 20. Similarly, where yarns with relatively high filament count are desirable, the number of orifices may be between 200 and 400, and even more for higher decitex yarns.
With respect to the orifice diameter, it is generally contemplated that numerous diameters are suitable for spinning contemplated fibers, and the choice of a particular diameter will depend at least in part on the desired physical properties of the fiber. For example, contemplated orifice diameters include diameters between 0.8-2.3 mm, and even more. Further exemplary suitable orifice parameters may be found in U.S. Pat. No. 5,085,818 to Hamlyn et al., which is incorporated by reference herein.
It should further be appreciated that suitable polymeric multifilament yarns need not be restricted to yarns with 11 decitex/filament, but may also include a dimensionally stable polymeric multifilament yarn having a decitex per fiber count DPF of at least 7.5, more preferably of at least 9, even more preferably of at least 10, and most preferably of at least 12, so long as contemplated polymeric multifilament yarns are dimensionally stable. Thus, especially contemplated dimensionally stable yarns may have a DPF between 10 and 20. The term xe2x80x9cdimensionally stable yarnxe2x80x9d as used herein means that suitable yarns will have a dimensional stability defined by Ex+TS of no more than 12, and more preferably a dimensional stability defined by Ex+TS of no more than 11.
It is further contemplated that the filaments are spun into a delayed quench, and particularly contemplated that the temperatures of the gaseous atmosphere in the delayed quench are generally above 250xc2x0 C. Solidification of the extruded filaments is preferably performed in an air quenching column at a quench rate of preferably between about 10 mm (H2O) and about 70 mm (H2O). However, it should be appreciated that numerous quench rates below 10 mm (H2O) and above 70 mm (H2O) are also suitable (e.g., 2-10 mm and less, or 70-120 mm and even more)
Thus, it should be appreciated that the undrawn yarn that is formed by contemplated filaments will be a dimensionally stable yarn precursor with a birefringence xcex94n of at least 0.020, so long as such xcex94n values are indicative of dimensional stability of at least first generation.
In further contemplated aspects of this inventive subject matter, an adhesion active overfinish may be applied to the undrawn yarn, the drawn yarn, or both. Typical adhesion active finish additives include polyglycidyl ethers (U.S. Pat. Nos. 4,462,855; 4,557,967; and 5,547,755, all of which are incorporated by reference herein), multifunctional epoxy silanes (U.S. Pat. No. 4,348,517, incorporated by reference herein), and additives which form epoxides in situ (U.S. Pat. No. 4,929,760, incorporated by reference herein).
In still further contemplated aspects of the inventive subject matter, contemplated undrawn yarns are drawn in a series of draw rolls, and a typical draw configuration includes four to five roll pairs Z1-Z5. While Z1 may be heated to various temperatures, it is generally preferred that Z1 is heated to between about 20xc2x0 C. and 120xc2x0 C., more preferably between about 40xc2x0 C. and 80xc2x0 C. Temperature of Z3 may vary widely from 60xc2x0 C. to 250xc2x0 C. depending on whether Z4 has much higher speed (stretching between rolls) or similar speed (primarily heat-setting between rolls). Lower temperatures are preferred where substantial additional stretching occurs between the rolls. With respect to the final godet roll pair, Z4 (for 4-roll pair panel) or Z5 (5 roll pair panel), it is contemplated that preferred temperatures are in the range of about 120xc2x0 C. to 160xc2x0 C. Contemplated draw ratios of the multifilament fibers will typically be in the range of about 1.2-2.5. Further especially suitable materials and spinning/drawing conditions are described in U.S. Pat. Nos. 5,067,538 and 5,234,764 to Nelson, both of which are incorporated by reference herein.
In a further contemplated aspect of the inventive subject matter, contemplated yarns may be twisted into cords of various configurations using procedures and equipment well known in the art. For example, especially contemplated configurations include 1100/2 decitex cords with relatively low twist of between 270xc3x97270 to 320xc3x97320 to cords with relatively high twist of between 420xc3x97420 to 470xc3x97470 (and even higher). Equivalent twists for other deniers can be determined by keeping the twist multiplier constant (Sqrt(nominal cord decitex)xc3x97twist(tpm)).
Thus, a method of forming a yarn may comprise a step in which a polymeric material is provided and a plurality of filaments is spun from the polymeric material. In another step, a dimensionally stable yarn is drawn from the plurality of filaments, wherein the yarn has a decitex per fiber count DPF of at least 7.5 and a fatigue strength retention FR, wherein the yarn is spun and drawn such that FR increases when DPF increases. Such prepared cords may find use in numerous applications and products, and particularly suitable applications and products include power transmission belts, automobile tires, safety belts, parachute harnesses and lines, cargo handling and safety nets, etc.